It happens very easily, that a camera gets tilted/panned when you are working in the corresponding viewport. Nothing can prevent this behaviour. So i would like to suggest: When a camara and its target are frozen (or on a frozen level), the correspondent viewport is locked for change. No mouse action, no pan- or orbittool etc. should work (with exception of manipulating the coordinate input fields, which would be very intenionally!) and the viewport label should state [frozen] similar the [disabled] when the vieport is disabled.
Thanks for taking this into consideration!
Stephan
